Torque-demand-control type controllers disclosed, for example, in Patent Literature 1 to 4 that are described hereunder are known as controllers for an internal combustion engine. In the case of a torque-demand-control type controller, an actuator is operated based on a requested torque. If the internal combustion engine that is the object of control has a turbo-supercharger with a waste gate valve, torque control can be performed through coordinated operations by the waste gate valve and a throttle. In such case, a pressure upstream of the throttle is controlled by operation of the waste gate valve, and an intake air amount is controlled by operation of the throttle.
In this connection, in addition to a driver-requested torque that is calculated based on the degree of opening of an accelerator pedal, requested torques with respect to an internal combustion engine also include requested torque from various on-board systems such as a traction control system, a vehicle stability control system, and an electronically controlled automatic transmission. In many cases, a system-requested torque that such on-board systems request is a torque that changes quickly in comparison to a driver-requested torque. For example, when an upshift operation is performed by an electronically controlled automatic transmission, a torque that changes in a pulse shape in a torque decreasing direction is requested from the internal combustion engine by the electronically controlled automatic transmission.
FIG. 4 illustrates control results in a case where, in the case of a conventional controller that subjects a waste gate valve and a throttle to coordinated operations, torque is requested that changes in a pulse shape in a torque decreasing direction in accordance with a period of transmission control of an electronically controlled automatic transmission. According to this conventional controller, when the requested torque changes, a target supercharging pressure relating to control of the waste gate valve is changed in accordance therewith, and a target degree of throttle opening relating to control of the throttle is also changed. Consequently, in a case where the requested torque changes in a pulse shape in a torque decreasing direction, a target supercharging pressure and a target degree of throttle opening are also caused to change in a pulse shape in a decreasing direction, respectively.
The responsiveness of the actual supercharging pressure with respect to an opening operation of the waste gate valve is high, and the actual supercharging pressure decreases rapidly to track a decrease in the target supercharging pressure. Furthermore, the responsiveness of the actual intake air amount with respect to a closing operation of the throttle is also high, and the actual intake air amount decreases rapidly to track a decrease in the target degree of throttle opening. That is, according to the conventional controller, in a case where the requested torque decreases in a step shape at a time point t1, since the intake air amount can be caused to decrease to track the step-shaped change, the step-shaped torque decrease that was requested can be achieved with respect to the actual torque.
However, because of the characteristics of a turbo-supercharger, the responsiveness of the actual supercharging pressure with respect to a closing operation of a waste gate valve is not high, and there is a delay in increasing the actual supercharging pressure with respect to an increase in the target supercharging pressure. Unless a supercharging pressure that acts upstream of the throttle increases, it is difficult for the intake air amount to increase irrespective of how much the throttle is opened. Consequently, an increase in the actual intake air amount with respect to an increase in the target degree of throttle opening is delayed. That is, according to the conventional controller, in a case where the requested torque increases in a step shape at a time point t2, it is difficult to rapidly increase the intake air amount to track the step-shaped change, and it is thus difficult to achieve the requested step-shaped torque increase in the actual torque.
As described above, according to the conventional controller, in a case where a pulse-like torque change in a torque decreasing direction is requested, although the torque can be caused to decrease in a step shape, it has been difficult to immediately thereafter increase the torque in a step shape. This problem is not limited to only a controller that subjects a waste gate valve and a throttle to coordinated operations. The problem also applies to a controller that takes a supercharged engine with a variable displacement-type turbo-supercharger as a control object, and subjects the variable displacement-type turbo-supercharger and a throttle to coordinated operations. It is also a problem that applies in general to torque-demand-control type controllers that subject two kinds of actuators that are provided upstream and downstream in an intake passage to coordinated operations based on a requested torque, such as a controller that subjects a throttle and an intake valve with a variable lift mechanism to coordinated operations.